Fuel conversion reactor

ABSTRACT

A conversion reactor ( 10 ) including an outer shell ( 12 ) having first ( 14 ) and second ( 16 ) ends and an inner surface ( 16 ) a primary inner shell ( 30 ) extending into the outer shell ( 12 ), the primary inner shell ( 30 ) defining a heat exchanging chamber ( 100 ) and having primary and secondary ( 34 ) ends, and a secondary inner shell ( 40 ) having a first end ( 42 ) located adjacent the secondary end ( 34 ) of the primary inner shell ( 30 ). One or more oulet apertures ( 46 ) are formed between the two inner shells ( 30,40 ) for passage of the gaseous fluid out of the heat exchanging chamber ( 100 ). There are also a plurality of heat exchange tubes ( 50 ) extending through the heat exchanging chamber ( 100 ) between first ( 58 ) and second ( 64 ) tube sheets and connected to same. The first tube sheet ( 58 ) is mounted in the primary inner shell ( 30 ) while the second tube sheet ( 64 ) is connected to the secondary inner shell ( 40 ). The adjacent ends ( 42,34 ) of the inner shells ( 40,30 ) form a disconnected joint and the secondary inner shell is free to move relative to the primary inner shell upon thermal expansion of the tubes ( 50 ).

FIELD OF THE INVENTION

This invention relates to fuel conversion reactors, and morespecifically to burners and fuel reformers for use in fuel cell systems.

BACKGROUND OF THE INVENTION

The use of fuel cells has become of increasing interest in recent yearsfor the application of power generation by means of a stationaryinstallation and for purposes of transportation where the fuel cell istransported with the vehicle. The fuel of these fuel cells is commonlyhydrogen that has been produced by reacting a hydrogen-containing fuel,usually a hydrocarbon or a low molecular weight alcohol, over one ormore catalysts in a fuel reformer.

There are a number of known processes for generating hydrogen fromhydrogen-containing fuels in a fuel reformer. A first known process forconversion of hydrogen-containing fuels to hydrogen is known as “steamreformation”, which is conducted at elevated temperatures. In the caseof a hydrocarbon fuel, steam reformation proceeds via the followingreaction, which is generally endothermic:C_(n)H_(m)+nH₂O?nCO+(m/2+n)H₂.

One difficulty with steam reformation is that external heat may berequired to drive the reaction forward to produce hydrogen and carbonmonoxide. External heat can be supplied to the steam reformationcatalyst from a number of sources, and is transmitted to the catalystbed using heat exchangers. Some of the external heat may be supplied bypassing the high temperature reformate produced by the catalytic steamreformation through a regenerative heat exchanger, thereby returningsome of the heat of the high temperature gas to the endothermicreforming reaction. Alternatively, the external heat may be generated bycombustion of anode off-gases and/or other fuels in a burner. Thecombustion reaction taking place in the burner can be catalyzed ornon-catalyzed. Examples of catalytic and non-catalytic burners aredescribed in U.S. Pat. No. 6,232,005 issued to Pettit.

A second known process for converting hydrogen-containing fuels tohydrogen is known as “partial oxidation”, which proceeds via thefollowing exothermic reaction:C_(n)H_(m)+n/2O₂?nCO+m/2H₂.

Partial oxidation can be performed at high temperatures (about 1200 to1500° C.) without a catalyst, or can be performed with a catalyst atmuch lower temperatures, typically about 500 to 800° C. One disadvantageof partial oxidation is that it produces less hydrogen per molecule ofhydrogen-containing fuel than steam reformation, since some of the fuelis consumed by oxidation. Since the oxidation is exothermic, there is noneed for the provision of external heat through a heat transfer surface.

A third known process for converting hydrogen-containing fuels tohydrogen is “autothermal reformation”, in which fuel, water and oxygen,usually in the form of air, are reacted in the presence of a catalyst togenerate a hydrogen-rich fuel gas. Autothermal reformation can be viewedas a combination of two reactions, an exothermic partial oxidation andan endothermic steam reformation, with the net heat of reaction beingdetermined by the ratios of oxygen to fuel and water to fuel. Generally,these ratios are established so that the net heat of reaction isslightly exothermic, thereby eliminating the need for application ofexternal heat, resulting in a relatively simple system design whichmakes autothermal reforming attractive for practical applications.

As can be seen from the chemical reactions depicted above, considerableamounts of carbon monoxide are produced during conversion of thehydrogen-containing fuel. To avoid poisoning of the fuel cell, the levelof carbon monoxide in the reformate must be reduced to a low level. Thisis particularly true for proton exchange membrane (PEM) fuel cells,which have a low tolerance for carbon monoxide. Thus, the reformate istypically subjected to at least one “carbon monoxide cleanup” reaction,which preferably comprises one or more water/gas shift reactions and/ora preferential oxidation reaction, in which carbon monoxide present inthe reformate is consumed in a catalytic reaction with oxygen or water(steam).

Regardless of the specific conversion process utilized, significantthermal stresses are exerted on fuel conversion reactors, which can havea detrimental effect on durability. Designers of such reactors havetherefore sought to reduce thermal stresses in the mechanical design ofthese units.

There are two conventional design approaches to overcome the problem ofthermal stress in a fuel conversion reactor. The first is to reduce thestress levels by permitting thermal expansion of components of thereactor, and the second is to increase the strength of the reactorstructure or the materials used in the structure so that the maximumoperating stress will not exceed the maximum design strength.

One well known type of heat exchanger that is used in a wide variety ofapplications including boilers and other high temperature heatexchangers is known as the “tube bundle” structure, also called a “shelland tube” heat exchanger. Reference can be made to sections 3.1.2. and4.2.3 of the Heat Exchanger Design Handbook, 1998, by G. F. Hewitt for adiscussion of this type of heat exchanger. There are a variety of suchheat exchangers including a fixed tube sheet or fixed head type. In thistype there is an exterior metal shell which can, for example, becylindrical and mounted within this shell are two spaced apart tubesheets on which a number of tubes are mounted. There are head covers orcomplete heads or channel covers at each end, which serve as fluidmanifolds. With such a heat exchanger, the thermal expansioncoefficients of the shell and the tubes during operation can cause adifferential movement between them. Excessive movement of this type cancause the tubes to loosen in the tube sheets. One known way forovercoming the problem of differential movements is to provide a shellexpansion bellows.

U.S. Pat. No. 5,382,271 issued Jan. 17, 1995 to Industrial TechnologyResearch Institute, describes a compact tube and shell structure forhydrogen generation where a catalyst is used in the water-shift reactionin order to reduce the level of carbon monoxide in the outflowing gases.Two tube sheets are mounted near opposite ends of a cylindrical shelland first and second sets of partition plates are mounted between thetube sheets. A plurality of tubes extend between the tube sheets andthrough the partition plates. There is a porous metal layer arrangedimmediately below the upper tube sheet and then catalyst material isarranged below this layer. There is an exhaust gas chamber and anexhaust outlet provided below the bottom tube sheet. Combustible gasflows into the shell body by means of an inlet in the upper end. A feedinlet is located in one side of the shell body just below the upper tubesheet. For certain types of hydrocarbons, a catalyst used for the steamreforming step is placed in the middle section while another catalystused in the last section just above the bottom tube sheet is for thewater-gas shift reaction.

With this known device, combustible gas enters the upper chamber formedin the shell above the upper tube sheet and, after combustion, theexhaust gas at a very high temperature passes through the tubes in orderto enter an exhaust gas chamber at the bottom. The heat of the exhaustgas is transferred to the porous metal layer and the catalyst(s) whilethe exhaust gas passes through the tubes. This heat exchange alsodecreases the temperature of the exhaust gas. With this known hydrogengenerator structure, there can be a thermal expansion problem if thetubes expand at a different rate than the shell as the tubes areapparently rigidly mounted in the tube sheets which in turn are rigidlymounted in the shell.

SUMMARY OF THE INVENTION

According to one aspect of the invention, the reactor comprises a fuelconversion reactor including a shell-and-tube heat exchanger forpreheating a gaseous fluid prior to catalytic or non-catalytic reactionwith a fuel. The heat exchanger includes a primary shell member havingprimary and secondary ends and a side wall extending between these endsand defining a heat exchanging chamber located within the shell member.There is an inlet for introducing the gaseous fluid into the heatexchanging chamber, a first tube sheet fixedly mounted on the primaryshell member in the vicinity of the primary end and sealingly closingthe heat exchanging chamber at one end of the chamber, and a second tubesheet device which is separate from the primary shell member and islocated in the vicinity of the secondary end. The second tube sheetdevice forms another end of the chamber that is opposite the one end ofthe chamber. A plurality of heat exchange tubes extend from the firsttube sheet to the second tube sheet device and are rigidly connected toboth the first tube sheet and the second tube sheet device. These heatexchange tubes provide passageways for the gaseous mixture to flowinside the tubes through the heat exchanging chamber. One or moreoutlets are formed in at least one of the primary shell member and thesecond tube sheet device in the region of the secondary end of theprimary shell member in order to provide at least one outlet for thegaseous fluid which flows through the heat exchanging chamber on a shellside thereof during operation of the fuel conversion reactor.

Preferably, the reactor includes an outer shell having first and secondends and an outer shell wall extending between these ends. The outershell is closed at the second end, extends around the primary shellmember and the second tube sheet device, and has an inlet for the fuel.A fuel passageway is formed between the outer shell wall and the sidewall of the primary shell member and extends from the inlet for the fuelto the one or more outlet apertures.

Preferably, the second tube sheet device includes a secondary shellmember having a peripheral side wall with a first end of the secondaryshell member located adjacent the secondary end of the primary shellmember. The first end of the secondary shell member and the secondaryend of the primary shell member form a disconnected joint and thus thesecond tube sheet device is free to move relative to the primary shellmember upon thermal expansion of the heat exchange tubes.

According to another aspect of the invention, a method of converting afuel to a hot gaseous mixture comprises providing a heat exchangingshell apparatus defining a heat exchanging chamber and having aplurality of heat exchange tubes mounted therein so that each extendsthrough said chamber, these tubes providing passageways for flow of thehot gaseous mixture. A gaseous fluid to be reacted with the fuel isintroduced into the heat exchanging chamber and passes through thechamber, thereby causing the gaseous fluid to be heated by heat exchangewith the hot gaseous mixture flowing through the tubes. The heatedgaseous fluid is withdrawn from the chamber and is mixed with the fuelto provide a mixture of the fuel and the gaseous fluid. This initialmixture is reacted, optionally in the presence of a catalyst, to producethe hot gaseous mixture.

In some preferred embodiments of the invention, the reactor comprises aburner in which the fuel undergoes a catalytic or non-catalyticcombustion reaction with a gaseous fluid containing oxygen, therebyproducing a hot, gaseous mixture of combustion gases from which usableheat may be extracted.

In other preferred embodiments of the invention, the reactor comprises afuel reformer in which a hydrogen-containing fuel undergoes a fueltransformation reaction with a gaseous fluid to produce a hot gaseousmixture containing hydrogen which may, for example, be utilized in afuel cell engine. The fuel transformation reaction may preferablycomprise a steam reformation, catalytic or non-catalytic partialoxidation, or an autothermal reformation process, with autothermalreformation being particularly preferred for the reasons mentionedearlier. The gaseous fluid to be reacted with the hydrogen-containingfuel preferably contains water or steam and/or an oxidant such asmolecular oxygen (referred to herein as “oxygen”), depending on the fueltransformation reaction used. With the exception of non-catalyticpartial oxidation, the gaseous fluid and the hydrogen-containing fuelare reacted in the presence of a suitable catalyst.

In yet another aspect, the present invention provides in a fuelconversion reactor, a shell-and-tube heat exchanger for heating agaseous fluid prior to reaction with a fuel and for cooling a gaseousmixture produced by the reaction, said heat exchanger comprising: (a) afirst heat exchanger section comprising: (i) a first primary shellmember having primary and secondary ends and a sidewall extendingbetween said ends and defining a first heat exchanging chamber locatedwithin the first shell member; (ii) a first tube sheet fixedly mountedon said primary shell member in the vicinity of said primary end andsealingly closing said first heat exchanging chamber at one end of thefirst chamber; (iii) a second tube sheet device which is separate fromsaid primary shell member and is located in the vicinity of saidsecondary end, said second tube sheet device forming another end of saidfirst chamber that is opposite said one end of the first chamber; and(iv) a plurality of heat exchange tubes extending from said first tubesheet to said second tube sheet device and rigidly connected to both thefirst tube sheet and the second tube sheet device, said heat exchangetubes providing passageways for said gaseous mixture to flow inside thetubes through said first heat exchanging chamber; and (v) one or moreoutlet apertures formed in the region of said secondary end of saidprimary shell member in order to provide at least one outlet for saidgaseous fluid which flows through said first heat exchanging chamber ona shell-side thereof during operation of said fuel conversion reactor;and (b) a second heat exchanger section comprising: (i) a second primaryshell member having primary and secondary ends and a sidewall extendingbetween said ends and defining a second heat exchanging chamber incommunication with the first heat exchanging chamber, the second shellmember being concentric with the first shell member with the primary endof the first shell member being located proximate the secondary end ofthe second shell member; (ii) a plurality of heat exchanging tubesmounted in the second shell member and communicating with the heatexchange tubes of the first heat exchanger section; (iii) an inlet inthe sidewall of the second shell member for introducing the gaseousfluid into the second heat exchanging chamber; (iv) one or more outletapertures formed in the region of the secondary end of the second shellmember to provide at least one outlet for the gaseous fluid to flow fromthe second heat exchanging chamber to the first heat exchanging chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from the followingdetailed description of preferred embodiments of the invention taken inconjunction with the accompanying drawings, in which:

FIG. 1 is an axial cross-section of a preferred form of fuel conversionreactor, comprising a fuel reformer constructed in accordance with theinvention;

FIG. 2 is a perspective view showing one side of and the top of the fuelreformer of FIG. 1, this view having the outer shell partially brokenaway in order to illustrate details of the inner shells;

FIG. 3 is a cross-sectional detail taken along the line III-III of FIG.2, this view showing the disconnected joint between the two innershells;

FIGS. 4 a and 4 b are horizontal cross-sections taken along the lineIV-IV of FIG. 1;

FIG. 5 is an axial cross-section of an alternate embodiment of a fuelconversion reactor, comprising a fuel reformer wherein the fuel is notpreheated by the reformer itself;

FIG. 6 is a cross-sectional detail similar to FIG. 3 but showing anotherform of outlet apertures formed in the primary inner shell;

FIG. 7 is a cross-sectional detail similar to FIG. 3 but showing analternate embodiment wherein outlet apertures are formed in a secondaryinner shell;

FIG. 8 is a cross-sectional detail similar to FIG. 3 but showing afurther embodiment wherein outlet apertures are formed in the primaryinner shell and the secondary inner shell is formed with a sleeveextension;

FIG. 9 is another cross-sectional detail of the embodiment of FIG. 8 butshowing the two inner shells in a different or initial position;

FIG. 10 is a further cross-sectional detail similar to FIG. 3 butshowing another embodiment wherein outlet apertures are formed in thesecondary inner shell and the primary inner shell is formed with asleeve extension;

FIG. 11 is a further cross-sectional detail similar to FIG. 3 butshowing another embodiment wherein a single, continuous outlet apertureis formed between the primary and secondary inner shells;

FIG. 12 is a perspective view similar to FIG. 2 but showing an alternateform of projections on the outer shell;

FIG. 13 is a cross-sectional detail taken along the line XII-XII of FIG.12, this view showing the use of annular corrugations around a dimpleprojection;

FIG. 14 is an axial cross-section of a further alternate embodiment of afuel conversion reactor, comprising a fuel reformer wherein the secondcatalyst bed is eliminated;

FIG. 15 is an axial cross-section of a single shell fuel conversionreactor according to a further alternate embodiment of the presentinvention;

FIG. 16 is an axial cross-section of an integrated fuel conversionreactor according to the present invention;

FIG. 17 is an axial cross-section of an integrated fuel conversionreactor according to another embodiment of the present invention;

FIG. 18 is a cross-sectional detail similar to FIG. 6 showing discreteoutlet apertures formed in the primary inner shell of the first heatexchanger section of the fuel conversion reactor shown in FIG. 17; and

FIG. 19 is an axial cross-section of an integrated fuel conversionreactor according to yet another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred fuel conversion reactors according to the invention aredescribed below as fuel reformers. However, it will be appreciated thatany of the preferred structures described below may be equally suitable,with minor modifications, for use as catalytic or non-catalytic burners.

FIG. 1 illustrates a first preferred fuel reformer 10 according to theinvention, which is constructed for the purpose of convertinghydrogen-containing fuel to hydrogen gas by means of an autothermalreformation process in which a gaseous fluid containing steam and oxygenor an oxygen-containing gas such as air undergoes a catalyzed reactionwith a hydrogen-containing fuel. Where the hydrogen-containing fuelcomprises a hydrocarbon, the following catalyzed reactions take place inthe fuel reformer 10:

(1) Partial Oxidation (exothermic)C_(n)H_(m)+n/2O₂?nCO+m/2H₂

(2) Steam Reformation (endothermic)C_(n)H_(m)+nH₂O?nCO+(m/2+n)H₂

As mentioned above, the two steps of the autothermal reformation takeplace in the fuel reformer 10 without spatial separation, and preferablytake place simultaneously in the same catalyst bed or structure.

The preferred illustrated reformer 10 includes an outer shell 12 havinga first end 14 and a second end 16. The shell has a cylindrical innersurface 18 and a cylindrical external surface 20 which extend betweenthe first and second ends. The second end is closed by means of a topcap member 22 which is fixedly attached to the cylindrical, main body ofthe outer shell. As shown in FIGS. 2 and 4 a, there are inwardlyextending projections in the form of longitudinally extending ribs 24formed in the outer shell and these are provided for the purposeexplained hereinafter. The bottom ends of the ribs are spaced away fromthe bottom or first end 14 of the outer shell.

An alternate construction of the fuel reformer 10 is illustrated inFIGS. 12 and 13. This embodiment is the same as that shown in FIG. 2except that the outer shell 12 has inwardly extending projections in theform of round dimples 25, which serve the same purpose as the ribs 24.As shown in FIG. 12, the dimples 25 may be arranged in longitudinallyextending rows, although other arrangements are possible. Although theillustrated dimples are round, obviously other shapes such as ellipticalor oblong are also possible. In order to allow for thermal expansion ofa primary inner shell 30 relative to the outer shell 12, each dimple maypreferably be surrounded by one or two annular corrugations 31 whichwill allow the inner end of the dimple to be pushed outwardly by theinner shell 30 as it expands, although other arrangements are possible.In a similar manner, the ribs 24 in the embodiment of FIG. 2 can also besurrounded by one or two corrugations 33 for the same purpose. Anotheralternative construction is to provide the ribs or dimples on theprimary inner shell 30 (and also on a secondary inner shell 40 describedbelow), in which case the ribs or dimples project outwardly to engagethe inner surface of the outer shell 12.

FIG. 4 b illustrates an alternative to the use of corrugations 33. InFIG. 4 b, the outer shell 12 is provided with inwardly extending ribs24′ of reduced height, such that the primary inner shell 30 is not incontact with some or all of the ribs 24′ before the reformer 10 hasreached operating temperature. As the reformer heats up and the innershell expands outwardly, it preferably makes contact with at least someof the ribs 24′, thereby centering the inner shell 30 within the outershell 12 as in FIG. 4 a. It will be appreciated that this type ofarrangement could also be used in the type of reformer in which ribs 24are replaced by dimples 25.

A first inlet 26 for the hydrogen-containing fuel is formed in the outershell in the vicinity of the first end 14. It will be understood thatthis inlet is connected by a suitable hose or pipe (not shown) to asupply of hydrogen-containing fuel which can be any one of a variety oftypes suitable for hydrogen production. For example, thehydrogen-containing fuel may comprise a hydrocarbon fuel selected fromone or more petroleum fractions such as gasoline, naphtha, kerosene,diesel fuel, etc.; natural gas or one or more components thereof,including methane, ethane, propane, etc. Alternatively, thehydrogen-containing fuel may comprise one or more alcohols such asmethanol and ethanol. Preferred hydrocarbon fuels are gasoline andmethane. The flow of fuel through the inlet 26 can be controlled by anysuitable means, such as by a throttle or control valve, to meet the fuelcell engine load demand.

Extending into the outer shell is the primary inner shell 30 which has aprimary end 32 and a secondary end 34. An outer surface 36 extendsbetween the primary and secondary ends. It will be understood that theprimary inner shell 30 is rigidly attached to the outer shell 12 at thefirst end 14 of the outer shell. The two shells can be attached at thislocation by welding or brazing. It will be seen that the inner shell 30extends into the open first end 14 of the outer shell and projects asubstantial distance into the outer shell. A fuel passageway 38 isformed between the outer surface 36 of the inner shell and the innersurface 18 of the outer shell and extends longitudinally from the inlet26 to the secondary end 34 of the primary inner shell. When theaforementioned ribs 24 are formed on the outer shell, the fuelpassageway 38 can comprise a plurality of separate sub-passageways 38 aas illustrated in FIG. 4 a. Since the ribs do not extend all of the waydown to the level of the inlet 26, the bottom ends of thesesub-passageways are interconnected to permit the fuel to flow completelyabout the inner shell and then upwardly through all of thesub-passageways. The location and shape of the ribs may be varied fromthat shown in FIG. 2. One skilled in the art will appreciate that theribs or the dimples can be arranged so as to provide uniform flowdistribution around the circumference of the shell to the maximum extentpossible.

The preferred reformer 10 also has a secondary inner shell 40 which hasa first end 42 located adjacent the secondary end 34 of the primaryinner shell. The inner shell 40 also has a second end 44 spaced from thefirst end 42 and located away from the top or second end 16 of the outershell. The preferred secondary inner shell 40 is also cylindrical likethe inner shell 30 and it has the same external diameter. The secondaryinner shell 40 can be substantially lower in height compared to theprimary inner shell 30. At least one and preferably a plurality ofoutlet apertures 46 are formed between the primary inner shell 30 andthe secondary inner shell 40 or in one of these two shells and areprovided for passage of the gaseous fluid out of the primary innershell.

As mentioned above, the gaseous fluid may preferably comprise a mixtureof steam and air, with the relative concentrations of air and steam inthe gaseous fluid preferably being adjustable by external means topermit the reformer to operate under a variety of conditions. Forexample, during start-up of the reformer, the gaseous fluid may becomprised entirely or primarily of air, resulting in catalyticcombustion of the hydrogen-containing fuel and rapidly heating thereformer and the catalyst(s) to a predetermined temperature. Once thetemperature reaches a sufficient level, the concentration of steam inthe gaseous fluid is increased, thereby increasing the hydrogen outputof the reformer.

The gaseous fluid enters the primary inner shell through a second inlet48 provided in a side of the primary inner shell 30 in the vicinity ofthe primary end 32. It will be understood that the inlet 48 is connectedby means of a suitable hose or pipe (not shown) to a source or supplyproviding the gaseous fluid. For example, a mixture of steam and air canbe provided by a suitable boiler of standard construction. Though it ispossible to extend the outer shell 12 downwardly from the position shownin FIGS. 1 and 2 so that it is adjacent the primary end 32 of the innershell, it is preferable to terminate the outer shell just above theinlet 48. This simplifies the structure of the reformer and helps toreduce thermal stress. Also, by this construction, one avoids the needto pass the inlet 48 through the walls of two shells. It will beunderstood that the amount of the gaseous fluid delivered through theinlet 48 can be made proportional to the amount of fuel being deliveredto the reformer, with means preferably being provided outside thereformer to control the composition of the gaseous fluid.

The illustrated apertures 46 of FIG. 2 are elongate in thecircumferential direction but are relatively short in the axialdirection. As will be seen hereinafter, the outlet apertures can becomelarger in size and can become interconnected as a result of longitudinalthermal expansion of heat exchange tubes 50 mounted in the reformer. Theapertures 46 of FIG. 2 are formed by castellations in the secondary end34 of the primary inner shell 30. However, it will be appreciated thatthe apertures may instead be formed by scallops or other shapes providedat the secondary end 34 of shell 30.

A further passageway 52 is formed between the secondary inner shell 40and the outer shell 12 and extends from the first end 42 to the secondend 44 of the secondary inner shell. Because the gaseous fluid flows outthrough outlets 46, it is mixed with the fuel just outside of theapertures and thus a mixture of the fuel and the gaseous fluid flowsthrough the further passageway 52 during use of the reformer. It is alsopossible to consider the passageway 52 an extension of the passageway38. As will be seen from FIG. 2, the ribs 24 can extend up to thelocation of the secondary inner shell 40 and thus the passageway 52 canalso comprise a number of sub-passageways that extend vertically as seenin FIGS. 1 and 2. It will be seen that the ribs 24 (and the dimples 25of the embodiment of FIGS. 12 and 13) function to properly center thetwo inner shells within the outer shell and hold the inner shells in thecorrect position and to strengthen the overall structure.

As illustrated in FIG. 1 and more clearly shown in FIG. 3, the secondaryend 34 of the primary inner shell and the first end 42 of the secondaryinner shell preferably form a disconnected joint at 54. Because the twoinner shells are not connected at this joint, the secondary inner shell40 is free to move relative to the primary inner shell 30 uponlongitudinal thermal expansion of the aforementioned heat exchange tubes50. Thus, the structure according to the invention accommodates thermalexpansion of the heat exchange tubes without increasing the gauge of themetal components and without resorting to the use of exotic materials.As well, the structure according to the invention is compact andprovides for integrated preheating of the fuel and/or the gaseous fluid,thereby providing benefits in terms of improved energy efficiency. Aswell, the structure of the reactor is adaptable to formation of compact,integrated structures in which both fuel transformation and carbonmonoxide cleanup reactions can be performed.

A first tube sheet 58 is fixedly mounted to the primary inner shell 30in proximity to the primary end 32 and this sheet sealingly closes offthe primary inner shell. This first tube sheet is preferably formed witha circumferential flange 60 for attachment and sealing purposes.Although the first tube sheet 58 is shown in the drawings as beingcircular, it will be appreciated that it may be of any suitable shape,for example oval, elliptical, rectangular, hexagonal, or any othermulti-faceted shape, depending on the shape of the primary inner shell30. The tube sheet is formed with a number of holes to receive the endsof an equal number of tubes 50 which can be rigidly attached to thistube sheet. The tubes 50 and the holes in tube sheet 58 are preferably,but not necessarily, circular. The tube sheet 58 can also be considereda bottom header of the reformer. The perimeter of the tube sheet can beattached to the inner surface of the inner shell 30 by any suitableknown means including brazing and welding.

As shown in FIG. 1, the primary inner shell 30 may be formed with aninwardly extending circumferential “lip” 59, or other inwardly extendingindentation(s), such as dimples, to correctly locate the first tubesheet 58 relative to the primary end 32 of the primary inner shell 30,and to form a bottom chamber to receive a catalyst 62. In the bottomchamber, a space sufficient in size is formed between the catalyst 62and the first tube sheet 58 to ensure that the catalyst receives auniform flow of reformate from tubes 50. In addition, a water or steaminsertion or mixing device may be inserted into the space to providewater for the reaction taking place in catalyst 62. This is discussedmore fully below in the context of FIG. 1.

The reformer also includes a second tube sheet 64 fixedly connected tothe secondary inner shell 40 and sealingly closing the interior of thesecondary inner shell. Again, the preferred tube sheet 64 has acircumferential flange 66 which can be brazed or welded to the innersurface of the inner shell 40 adjacent the first end 42. It will beunderstood that the second tube sheet also has a plurality of holes,preferably circular in shape, formed therein to receive the adjacentends of the tubes 50 and this tube sheet can be rigidly connected to theends of the tubes. In the illustrated preferred embodiment, the innershell 40 is formed with a circumferential lip 70 that projects inwardly.This lip can help correctly locate the tube sheet 64 and it can alsolocate and support a first catalyst 72 for the fuel transformationreaction. As shown in FIG. 1, the first catalyst is preferably mountedwithin the secondary inner shell 40 and also within the outer shell 12in the region of the second end 16. This catalyst 72 is preferably anautothermal reformation catalyst arranged for contact with the mixtureof the fuel and the gaseous fluid comprising steam and air in order toproduce the hot gaseous mixture.

A plurality of the aforementioned heat exchange tubes 50, only some ofwhich are shown in FIG. 1 for ease of illustration, extend from thefirst tube sheet 58 to the second tube sheet 64. These heat exchangetubes form passageways for the aforementioned hot gaseous mixture toflow from the first catalyst 72 through the second tube sheet 64, thenthrough the first tube sheet 58 and then to the catalyst 62, sometimesreferred to hereinafter as the second catalyst.

The second catalyst 62 is preferably a suitable catalyst for use in a“carbon monoxide cleanup” which, as described above, comprises either awater/gas shift reactions (3) and/or a preferential oxidation reaction(4), as follows:

(3) Water/Gas Shift (exothermic)CO+H₂O?CO₂+H₂

(4) Preferential Oxidation (exothermic)CO+½O₂?CO₂

Preferably, the second catalyst is a shift reaction catalyst, and morepreferably a high temperature shift reaction catalyst. If a water/gasshift reaction is to be the second catalytic reaction then water orsteam can be introduced into the fuel reformer at a point just below thetube sheet 58 and above the catalyst 62. This possibility is indicatedin FIG. 1 by the short inlet pipe 190 shown in dashed lines and thearrow labeled W. Although not shown in FIG. 1, it will be appreciatedthat a mixing device will preferably be received inside the bottomchamber between the tube sheet 58 and catalyst 62. The mixing device isattached to the end of water inlet pipe 190 and ensures evendistribution of the injected water or steam within the reformate forreaction in the catalyst 62. The mixing device effectively shortens thelength of the space between tube sheet 58 and catalyst 62 which wouldotherwise be required to achieve reasonable flow mixing and distributionof the injected steam or water.

The primary inner shell 30 is preferably open at its primary end 32 asillustrated so as to allow outflow of the reformate. Alternatively, asmaller outlet opening for the reformate can be formed at the bottom end32 of the inner shell and this outlet can be connected to one or morereactors in which the amount of carbon monoxide in the reformate isfurther reduced to an acceptable level, which may be less than 50 ppmdepending on the type of fuel cell being utilized. Where, for example,the carbon monoxide cleanup reaction conducted with the second catalyst62 comprises a high temperature shift reaction, the reformate maypreferably be subjected to one or more additional shift reactionsdownstream of the reformer 10, including at least one low temperatureshift reaction, and/or the reformate may be subjected to preferentialoxidation downstream of the reformer 10. After removal of carbonmonoxide, the resulting hydrogen gas product can be piped to a fuelcell, if desired.

The catalyst material 62 or 72 can be supported on various types ofstructures. The support structure may comprise one or more corrosion andheat resistant materials such as ceramics or refractory materials, andis in a form which promotes contact between the flowing gases and thecatalyst material within the reformer. Examples of support materialsinclude magnesia, alumina, silica and zirconia, and mixtures thereof,and the support structure may be in the form of beads or grids, forexample extruded ceramic monolith grids. In the alternative, thecatalyst support or the catalyst itself may comprise a corrugated,rolled metal foil which is mechanically assembled into the inner shellsection. The corrugated foil may, for example, be in the form of a slitand convoluted shape, such as a turbulizer. Where a metal foil is used,it is mounted in a manner known per se, so that it will not vibrate butwhich allows thermal expansion under the high temperature operatingconditions of the catalyst. In an alternative arrangement, some or allof the first catalyst may be contained inside heat exchange tubes 50,for example the catalyst material may be supported on the inner surfacesof the tubes 50 and/or on turbulizers contained within the tubes 50.Regardless of the form of the catalyst material or the supportstructure, the catalyst material is arranged so as not to undulyrestrict the flow of the fuel/gas mixture through the reformer. Thisarrangement of the catalysts (and as illustrated) allows the reformer tobe quite compact and reduces the overall length requirementssubstantially.

Preferably there are mounted on the tubes 50 a number of baffle platessuch as illustrated baffle plates 75, 76, 77. As shown in FIGS. 1, 4 a,4 b and 5, the edges of these plates are preferably in close proximityto, but not connected to the inner shell, and are rigidly connected toat least one and preferably a plurality of the tubes. One reason forconnecting the baffle plates to the tubes is to make the assemblyprocess easier. The baffle plates are preferably not connected to theinner shell so that the tubes 50 may expand longitudinally relative tothe inner shell.

The plates 75, 76, 77 are formed with openings, preferably circular inshape, through which the tubes 50 extend. The lowermost baffle plate 75is annular and has a large central opening 80 formed therein. Theoutermost tubes 50′ extend through the plate 75 near their bottom ends.The uppermost baffle plate 77 is also annular and has a large centralopening 82, with the outermost tubes 50′ extending through plate 77 neartheir top ends. The diameters of the uppermost baffle plate 77 andlowermost plate 75 are preferably such that there is no substantial flowof gases through the gap between the edges of plates 75, 77 and theprimary inner shell 30. The gap preferably does not exceed 1 mm. It willbe appreciated that the gap between plates 75, 77 and the primary innershell 30 is exaggerated in the drawings.

Baffle plate 76 is located between the bottom baffle plate 75 and thetop baffle plate 77 and a number of centrally located tubes 50 canextend through this plate although only one is shown in FIG. 1. Incontrast to the lowermost and uppermost baffle plates 75, 77, plate 76does not have a large central opening for passage of gases. Instead,plate 76 has a diameter such that a relatively large gap exists betweenthe edges of plate 76 and the primary inner shell 30, therebyencouraging flow of gases around the edges of plate 76. In this way, thebaffle plates 75, 76, 77 act to force the upflowing gaseous fluid toflow in a sinuous or winding manner to enhance the heat exchangeprocess, and to establish a good annular flow distribution for ejectionthrough the outlet openings 46. As shown by the curved arrows passingthrough the central opening 82 of top baffle plate 77 in FIG. 1, thegaseous fluid passing through the top baffle plate 77 flows radiallyoutwardly toward outlet openings 46. As it passes through the openings46, the gaseous fluid is uniformly mixed with the axially flowinghydrogen-containing fuel, in preparation for good radial flowdistribution of the mixed fluids prior to entering catalyst bed 72.

It will be appreciated that there may be more than three baffle platesin the heat exchanger, and that the baffle plates do not necessarilyhave a circular or annular shape as shown in the drawings. Rather, theplates can have any configuration which will enhance the heat exchangeprocess while maintaining adequate flow distribution.

It will be understood that the upward flowing steam and air is heated bythe downward flowing reformate passing through the tubes 50. As a resultof this exchange, the reformate is cooled as it passes downwardlythrough the tubes. Since the temperature of the reformate is much higherthan the mixture of steam and air, the thermal expansion of the tubes ismuch longer than the expansion of the inner shell 30. However, becausethe secondary inner shell 40 is free to move relative to the primaryinner shell 30, the greater expansion of the tubes 50 is accommodatedand thus there is no build up of thermal stress which could otherwisebreak the joint between the tubes and one or both of the headers or thejoint between the headers and the inner shell. It will also be seen thatbecause of the thermal expansion of the tubes, the outlet apertures 46vary in size during operation of the fuel reformer and these outletapertures in fact become larger as the length of the tubes 50 increases,thereby reducing the aperture flow resistance to effect either asustained or increased flow of gaseous fluid out of the primary innershell. This has the advantage of allowing a faster reforming process asthe reformer achieves optimum operating temperatures. It should be notedthat the gases flowing through the reformer are less dense as theirtemperature rises and the increased aperture size may partly compensatefor this.

It will be understood that in the preferred, illustrated fuel reformer,there is a hydrogen-containing fuel mixture delivery arrangement whichis adapted to deliver a mixture of the hydrogen-containing fuel and thegaseous fluid (comprising steam and air) to the first catalyst 72.Although this hydrogen-containing fuel mixture delivery arrangement cantake various forms, in the preferred illustrated embodiment of FIGS. 1and 2, this arrangement comprises the aforementioned outer shell member12 that extends around the primary and secondary shell members and isrigidly connected to the primary shell member. It will be appreciated,for example, that the incoming hydrogen-containing fuel can be heated bymeans other than that illustrated in FIGS. 1 and 2, for example by meansof heat exchange with the hot mixture of steam and air passing throughthe heat exchanging chamber 100. In another alternative constructionshown in FIG. 5, the fuel could simply be introduced directly into theupper chamber 102 where it can mix with the hot mixture of steam and airpassing out of the outlet apertures 46. The upper chamber 102 can beconsidered an enclosed mixing chamber that is adjacent the firstcatalyst 72. Although the fuel is not preheated inside the reformer ofFIG. 5, to it may be preheated elsewhere in the system. The fuelreformer shown in FIG. 5 may be the preferred configuration in terms ofsafety since the fuel and the oxygen-containing gas are combinedimmediately before they reach the catalyst 72.

The combination of the secondary inner shell 40 and the second tubesheet 64 can be considered a second tube sheet device which is separatefrom the primary shell member 30 and which is located in the vicinity ofthe secondary end 34. This second tube sheet device forms one end of theheat exchanging chamber 100. As illustrated, one end of the second tubesheet device which includes the secondary shell member 40 is locatedadjacent the secondary end 34 of the primary shell member.

If desired, a turbulizer, which per se is of known construction, can beinserted into the passageway 52 in order to ensure a very good mixing ofthe fuel and the steam and air. It will be understood that thisturbulizer is annular in shape and extends about the circumference ofthe secondary inner shell 40.

The sheet metal from which these fuel reformers are made must have asufficiently high melting point, elevated temperature strength, andoxidation resistance in order to achieve the necessary durability.Typical materials that can be used to construct this reformer includeaustenitic or ferritic stainless steel, Inconel™, and other nickel oralloy steel materials. The gauge of the sheet metal will depend on thedesign of the particular reformer system but can typically range from0.5 mm to 4 mm for low to moderate life requirements, or the gauge canbe doubled over this range for large or extended life applications (forexample, stationary power). The size of the fuel reformer of thisinvention can vary depending upon its intended use, it being understoodthat it is generally desirable to reduce the weight and spacerequirements of the reformer while maintaining the desired durablility.

For purposes of initial start-up of the illustrated fuel reformer, aseparate vaporizer (not shown) can be used to heat and vaporize the fuelsuch as gasoline so that the initial exothermic autothermal reformationcan commence. Once this reaction commences, because of the heat createdby the autothermal reformation process, the temperature of the system atthe catalyst 72 will increase quickly.

It may also be possible to use the gaseous fluid exiting the chamber 100to heat up the small amount of fuel that is used initially and therebyachieve a mixture temperature which is sufficiently high to start orfacilitate the start of the autothermal reformation reaction. Ifdesired, a catalytic or non-catalytic burner can be used to heat thegaseous fluid, at least for purposes of a cold start-up of the reformer.

The alternate fuel reformer 110 shown in FIG. 5 also differs from fuelreformer 10 in that the outer shell 112 is substantially shorter thanthe outer shell 12 in reformer 10. The outer shell 112 terminates at afirst or bottom end 114 which can be just below the apertures 46. Theouter shell is closed by means of a top cap member 122 which, unlike thecap member in the first embodiment, is formed with a central inlet 126for the flow of hydrogen-containing fuel into the reformer. As alreadydiscussed above, the fuel therefore flows directly into the upperchamber 102 where it is mixed with the gaseous fluid immediately beforepassing through the first catalyst 72. For some applications, the fuelcan enter the chamber 102 unheated or the fuel can be preheatedelsewhere by suitable known heating means (not shown). Extending intothe outer shell 112 is a primary shell 130 which can be similar in itsconstruction to the primary inner shell 30 of the first embodiment. Theshell 130 has an outer surface 136 which extends between the primary end32 and the secondary end 34. The primary shell 130 is rigidly attachedto the outer shell 112 at the first end 114 by means of welding orbrazing. In this embodiment the primary shell 130 extends only a shortdistance into the outer shell. The fuel reformer 110 also has asecondary shell 140 which is located within the outer shell 112. Thissecondary shell can be similar in its construction to the secondaryshell 40 of the first embodiment. There is a passageway 52 formedbetween the secondary shell 140 and the outer shell 112 and in apreferred embodiment it is a mixture of steam and air which passesupwards through this passageway to the mixing chamber 102. In thisembodiment there is also a disconnected joint at 54 formed between thesecondary end 34 of the primary shell 130 and the first or bottom end 42of the secondary shell 140.

It will be appreciated by those skilled in this art that the outletapertures formed in the region where the primary inner shell 30 meetsthe secondary inner shell 40 can be provided in various forms and someof these alternatives are illustrated in FIGS. 6 to 10 of the drawings.As illustrated in FIG. 6, a plurality of outlet apertures 150 can beformed in the primary inner shell 30 a short distance below thesecondary end 34. These apertures can be is rectangular as shown or theycan be other shapes such as circular or elliptical. Preferably theseapertures are distributed evenly about the circumference of the innershell 30 and preferably the outlet apertures are all of similar oridentical size. It will be understood that a butt joint or disconnectedjoint 54 is still provided in this embodiment, and may be used alone orin conjunction with additional apertures as shown in FIGS. 6 to 10.

In the alternative embodiment illustrated in FIG. 7, a plurality ofoutlet apertures 152 are formed about the circumference of the secondaryinner shell 40 and are spaced a short distance from its first end 42.The illustrated apertures are circular but again other shapes are alsopossible such as square, rectangular and elliptical. The apertures 152are preferably distributed evenly about the circumference of thesecondary inner shell. There may or may not be outlet apertures 170formed in the primary inner shell 30. Again, there is a butt ordisconnected joint provided at 54.

Turning to the embodiment illustrated by FIGS. 8 and 9, this embodimentis similar to that illustrated in FIG. 6 in that the primary inner shell30 is formed with a plurality of rectangular outlet apertures 150located a short distance from the secondary end 34. However, in thisembodiment, the upper or secondary inner shell 40 is formed with a shortsleeve extension 154. This sleeve extension extends about thecircumference of the inner shell 40 at the end adjacent to the secondaryend 34 of the primary inner shell. The sleeve extension 154 is coaxialwith a main peripheral side wall 156 of the inner shell 40. It will beunderstood that the peripheral side wall 156 has a first predetermineddiameter while the sleeve extension 154 has a second predetermineddiameter which is different from the first predetermined diameter and isin fact less than the first predetermined diameter in the embodimentillustrated in FIGS. 8 and 9. The sleeve extension 154 has a free end158 located in the region of the outlet apertures 150. It will beunderstood that, as in the above described embodiments, the secondaryshell member 40 is relatively movable during use of the fuel reformerbetween a first or initial position illustrated in FIG. 9 and a secondposition illustrated in FIG. 8. As shown in these figures, in the firstposition, the apertures 150 are partially blocked by the sleeveextension 154. However, as the fuel reformer heats up and the tubebundle expands, the inner shell 40 moves a short distance away from theprimary inner shell 30 and thus, as shown in FIG. 8, the apertures 150are at least substantially or entirely open for passage of the gaseousfluid out of the shell 30. In this embodiment, there is still adisconnected joint 160 but this joint is now formed between thesecondary end 34 of the inner shell 30 and the adjacent end of theperipheral sidewall 156. In this embodiment, the external diameter ofthe sleeve extension 154 is only slightly smaller than the internaldiameter of the inner shell 30.

Turning to the variation shown in FIG. 10, this embodiment is similar tothat shown in FIG. 7 in that the outlet apertures 152 are formed aboutthe circumference of the secondary inner shell 40 and are spaced a shortdistance from its first end 42. The primary inner shell 30′ is formedwith a coaxial sleeve extension 151 connected to its sidewall at theshell's secondary end 34. It will be seen that the primary inner shell30′ has an external diameter D₁ while the secondary inner shell has aninternal diameter D₂. The sleeve extension 151 has an external diameterD₃ as measured to exterior surface 153 which is different from theexternal diameter D₁ of primary inner shell 30′ and different from theinternal diameter D₂ of the secondary inner shell 40. In the preferredembodiment of FIG. 10, diameter D₃ is less than both diameters D₁ andD₂. The sleeve extension 151 has a free end 155 located in the region ofthe outlet apertures 152. As shown in FIG. 10, these apertures arepartially blocked by the sleeve extension 151, but as the fuel reformerheats up, these apertures are less blocked or entirely open for passageof gaseous fluid.

It will be appreciated that variations of these alternativeconstructions are possible. For example, instead of the sleeve extension154 of FIG. 9 or sleeve extension 151 of FIG. 10 being received insidethe opposing inner shell, it is possible to construct the sleeveextension 151 or 154 to have an internal diameter larger than theexternal diameter of the opposing inner shell, so that the end of theopposing shell is received inside the sleeve extension 151 or 154.Alternatively, it is possible to provide apertures in both the sleeveextension and in the opposing inner shell. When the fuel reformer iscold, the apertures of the sleeve extension and the opposing inner shellwould be only partially aligned, and as the fuel reformer warms up theapertures would be progressively brought into greater alignment with oneanother. Although alternative constructions are possible for the outletapertures, generally these outlet apertures will be located orpositioned adjacent to the butt or disconnected joint 54, 160.

As shown in FIG. 11, it is also possible to construct the reformer suchthat a single, continuous aperture 161 exists between the primary andsecondary inner shells. In such a construction, the tubes 50 are ofsufficient length to create the aperture 161 between the primary andsecondary inner shells, the gap 161 expanding in response tolongitudinal expansion of the tubes 50.

It will be appreciated by those skilled in the art of fuel reformingthat it is possible to construct a fuel reformer in accordance with thisinvention wherein one of the catalysts is omitted entirely and thereformer contains only the first catalyst 72 or the second catalyst 62.An example of such a fuel reformer 210 is illustrated in FIG. 14. Mostof the components of fuel reformer 210 are identical to the componentsdescribed above in connection with preferred fuel reformer 10, and areidentified by identical reference numbers. Fuel reformer 210 differsfrom fuel reformer 10 in that the second catalyst 62 is omitted fromfuel reformer 210. The preferred fuel reformer 210 may be utilized, forexample, where it is desired to perform all the carbon monoxide cleanupreactions downstream of the reformer 210.

Although the preferred embodiment shown in FIG. 14 is suitable for useas a fuel reformer, it may instead be used as a catalytic burner togenerate heat for use elsewhere in the fuel cell system, for example toheat steam for a fuel transformation reaction. The heat generated by theburner is preferably recovered downstream of the burner. In such anembodiment, the hydrogen-containing fuel may preferably be comprisedpartially or entirely of a fuel cell anode off-gas, which is reactedcatalytically with an oxygen-containing gaseous fluid to generate hotcombustion gases. Some of the heat contained in the combustion gases istransferred to the incoming fuel and gaseous fluid, and additional heatis preferably recovered by one or more heat exchangers which can eitherbe discretely separate units or which can be integrated with the burner.As mentioned earlier, the other preferred fuel reformers describedherein may also be similarly converted to catalytic burners.

As mentioned earlier, the preferred fuel reformers described herein canalso be converted to non-catalytic burners by omitting both catalystsfrom the reformer structure. In a non-catalytic burner according to theinvention, a hydrogen-containing fuel as in the catalytic burnerdescribed above is combusted with an oxygen-containing gaseous fluid inthe upper chamber (for example chamber 102 of FIG. 1) of the burner. Thehot combustion gases are then partially cooled by the incoming fuel andgaseous fluid as they pass through the tubes 50. The partially cooledcombustion gases then exit the burner, where they are preferably furthercooled by one or more additional heat exchangers which can either bediscretely separate units or which can be integrated with the burner.

FIG. 15 illustrates another preferred fuel reformer 300 according to thepresent invention which is also particularly useful as a catalytic ornon-catalytic burner, as described above. Most of the components of fuelreformer 300 are identical to the components described above inconnection with preferred fuel reformer 10, and are identified byidentical reference numbers. Fuel reformer 300 differs primarily fromthat shown in FIG. 1 in that it is of a single shell design, having anouter shell 312 extending between a first end 314 and a second end 316of the reformer 300. The reformer 300 has a single inlet through whichboth a hydrogen containing fuel and a gaseous fluid may be introducedinto the heat exchanging chamber 100. Alternatively, thehydrogen-containing fuel and the gaseous fluid may be introduced throughseparate inlets (not shown), including a configuration as in FIG. 5where the fuel is introduced through the top cap member 22.

In reformer 300, the hydrogen-containing fuel and the gaseous fluid aremixed inside the heat exchanging chamber 100, flowing around and throughbaffle plates 75, 76 and 77 and into annular passage 352 which connectsthe heat exchange chamber 100 to the upper chamber 102. The mixed fueland gaseous fluid are reacted as they flow through catalyst 72 toproduce hydrogen and carbon monoxide, preferably by an autothermalreformation. The hot reformate flows through tubes 50 and transfers someof its heat to the fuel and gaseous fluid flowing through the heatexchange chamber 100.

The annular passage 352 is formed between outer shell 312 and innershell 340 which is secured to second tube sheet 64. Thermal stresses areprevented by the lack of a secured connection between the inner shell340 and outer shell 312, thereby forming a disconnected joint wherebyaxial expansion of the tubes results in relative axial movement of theinner shell 340 relative to the outer shell 312.

Although reformer 300 is shown as comprising a reformer having twocatalysts 72 and 62, it will be appreciated that reformer 300 may alsobe used as a fuel reformer having a single catalyst, or may be used as acatalytic or non-catalytic burner, as described above. It will also beappreciated that reformer 300 may be provided with ribs 24, dimples 25or the like to centre the inner shell 340 within the outer shell 312, inthe manner described above with reference to the other preferredembodiments.

Also included within the scope of the present invention are integratedfuel conversion reactors in which two or more individual reactorsaccording to the invention are joined end-to-end to form integratedstructures. The integrated structures may preferably be formed bywelding or brazing the outer shells of the individual reactors. FIG. 16illustrates one preferred form of integrated reactor, comprising a fuelreformer 400 in which a reactor 402 similar to that shown in FIG. 1 andhaving a single catalyst 72 is coupled end-to-end with a reactor similarto that shown in FIG. 5 and having a pair of catalysts 72′ and 62. In aparticularly preferred embodiment, the catalyst 72 of reactor 402comprises a fuel transformation catalyst for converting ahydrogen-containing fuel to hydrogen, preferably an autothermalreformation catalyst. The catalysts 72′ and 62 of reactor 404 maypreferably comprise high and low temperature shift reaction catalysts,respectively. In this reactor 400, the hot reformate produced incatalyst 72 flows through tubes 50 of reactor 402 and into a mixingchamber 406 where it is combined with steam preheated in heat exchangechamber 100 of reactor 404. The carbon-monoxide depleted reformate flowsfrom catalyst 72′ through tubes 50 of reactor 404 where it is cooled byheat exchange with the steam in chamber 100, before entering catalyst 62for the low temperature shift reaction. Similarly, it is possible toprovide an integrated system which includes a preferential oxidationcatalyst.

Another form of integrated fuel conversion reactor 500 is illustrated inFIG. 17. As discussed in detail below, reactor 500 is designed to avoidsuper-cooling of reformate between the first catalyst 72 and the secondcatalyst 62 as may occur in heat exchangers 10 and 110 of FIGS. 1 and 5,under certain conditions. The temperature of the gaseous mixtureentering inlet 48 is a function of upstream system design and operatingconditions. As such, the temperature of the gaseous mixture may varysomewhat depending on the operating conditions. For example, in aspecific autothermal reformation system the temperature of the gaseousmixture entering inlet 48 may be about 180° C. under full loadconditions but may drop to about 160° C. under part load conditions. Theoperating temperature of the second catalyst 62, on the other hand, mayneed to be about 230° C. Thus, particularly under part load conditions,there is a possibility that the reformate passing between catalysts 72and 62 could be super-cooled by the gaseous mixture passing through heatexchanging chamber 100. This problem may be compounded if water is addedthrough tube 190 as in FIG. 1 due to the cooling effect of water.Super-cooling of reformate in prior art reactors has been avoided byprovision of a by-pass line and valve by which a portion of the gaseousmixture by-passes chamber 100 under part load conditions. However, thevalve and lines add complexity to the fuel reformer and exposure of thevalve to high temperatures can introduce valve durability or reliabilitylimitations.

The reactor 500 avoids super-cooling by providing an integratedstructure comprising a first heat exchanger section 502 having first andsecond catalysts 72 and 62 and a second heat exchanger section 504 intowhich the gaseous mixture is introduced and heated by the reformateflowing from the second catalyst 62. The structure and operation ofreactor 500 are now discussed in detail below.

The first heat exchanger section 502 of reactor 500 is similar instructure to the fuel conversion reactor 110 shown in FIG. 5, and likecomponents thereof are identified by like reference numbers. The firstheat exchanger section 502 includes a first catalyst 72 which maypreferably be an autothermal reformation catalyst and a second catalyst62 which may preferably comprise a carbon monoxide cleanup catalyst, forexample a shift reaction catalyst.

The second heat exchanger section 504 also has some similarity instructure to the fuel conversion reactor 110 shown in FIG. 5, havingtubes 50 extending between tube sheets 58 and 64 and with baffle plates75, 76 and 77 being provided on the tubes 50. The second heat exchangersection 504 has a primary shell 530 with an outer surface 536 and isprovided with an inlet 48 located proximate tube sheet 58 through whicha gaseous mixture enters heat exchanging chamber 506 to be heated byreformate leaving second catalyst 62 through tubes 50. Subject to thediscussion below, the primary shell 530 of second heat exchanger sectionmay comprise an extension of the primary shell 130 of the first heatexchanger section 502.

In the heat exchanger 500 shown in FIG. 17, the gaseous mixture enteringthe second heat exchanger section 504 through inlet 48 comprises fuel,air and steam. Accordingly, heat exchanger 500 is further distinguishedfrom heat exchangers 10 and 110 in that it does not include a separateinlet for fuel. It will however be appreciated that the heat exchanger500 could instead be provided with a separate fuel inlet analogous toinlet 26 in the outer shell 12 of heat exchanger 10 or inlet 126 in thetop cap member 122 of heat exchanger 110. Where heat exchanger 500 isprovided with a fuel inlet analogous to fuel inlet 26, it will beappreciated that the outer shell 112 would be extended downwardly as inFIG. 1.

An outer shell section 512 surrounds the lower portion of the first heatexchanger section 502 and the upper portion of the second heat exchangersection 504. The outer shell section 512 is rigidly attached at itsupper end 508 to the primary shell 130 of first heat exchanger section502 and is rigidly attached at its lower end 510 to the primary shell530 of the second heat exchanger section 504. Between its upper andlower ends 508, 510 the outer shell section 512 is spaced from the outersurfaces 136, 536 of the primary shells 130, 530 so as to form anannular passageway 552 for passage of the gaseous mixture of fuel, steamand air from the heat exchanging chamber 506 of the second heatexchanger section 504 to the heat exchanging chamber 100 of the firstheat exchanger section 502. The gaseous mixture enters the annularpassageway 552 through one or more openings 546 provided in the outershell 530 (or between shells 530 and 130) proximate tube sheet 64 ofsecond heat exchanger section 504 and leaves the annular passageway 552through one or more openings 548 provided in the outer shell 130 of thefirst heat exchanger section 502.

The structure of openings 546 and 548, as well as openings 550 proximatetube sheet 64 of first heat exchanger section 502, will now be discussedin detail. The openings 546, 548 and 550 can be in the form of discreteapertures formed in-shells 130 and 530 or can be in the form ofdisconnected joints similar in structure to disconnected joint 54. Wherea disconnected joint is provided, it will be appreciated that the jointcould have a structure as shown in any of FIGS. 1 and 5 to 10, includingthe apertures shown therein.

For example, FIG. 18 illustrates an embodiment in which openings 550comprise a plurality of discrete apertures 552 and no disconnected jointis provided. It is however preferred to provide a disconnected joint 54as illustrated in FIGS. 1 and 5 to 10 to accommodate longitudinalthermal expansion of the tubes 50 of the first heat exchanger section502.

The at least one opening 548 can also be in the form of discreteapertures formed in shell 130 as shown in FIG. 18 or a single,continuous opening 548 could be provided in the form of a disconnectedjoint whereby the portion of shell 130 located above opening 548 isdisconnected from the portion of shell below opening 548. Such adisconnected joint formed by opening 548 could have a structure as shownin any of FIGS. 1 and 5 to 10.

The at least one opening 546 is formed between the shell 130 of thefirst heat exchange section 502 and the shell 530 of the second heatexchange section 504. Opening 546 can be in the form of a plurality ofdiscrete apertures as shown in FIG. 18 such that the shell 530 forms anintegral extension of shell 130 and no disconnected joint is formed.Alternatively, a single continuous opening 546 could be provided suchthat shells 130 and 530 are separate from one another and a disconnectedjoint is provided. The disconnected joint formed by opening 546 couldhave a structure as shown in any one of FIGS. 1 and 5 to 10.

It is preferred that a disconnected joint be provided at one or more ofopenings 546, 548 and 550 so as to accommodate thermal expansion of theheat exchanger 500. More preferably, a disconnected joint is provided atleast at opening 550 so as to accommodate thermal expansion of the tubes50 of first heat exchanger section 502 caused by the relatively hightemperature reformate produced by first catalyst 72. Where adisconnected joint is provided at opening 550, the openings 546 and 548may preferably each comprise a plurality of spaced apertures. Theprovision of an additional disconnected joint at opening 546 or 548 isrelatively unimportant in this case since there is usually a relativelysmall temperature difference across, the second catalyst 62. It may alsobe preferred to provide disconnected joints at both of openings 546 and548, and eliminate the disconnected joint at opening 550. Wheredisconnected joints are provided at openings 546 or 548 they arepreferably “pre-spaced” as shown in FIG. 11 since the open area of thejoint will decrease due to thermal expansion of the tubes 50 in thefirst heat exchanger section 502. In this case it may be necessary toprovide slotted holes to avoid restriction of gas flow or apredetermination of an acceptable minimum gap.

FIG. 19 illustrates another example of an integrated fuel conversionreactor 600 which is similar in structure and operation to the reactor500 shown in FIG. 17, and like components are identified by likereference numbers. Fuel conversion-reactor 600 includes a first heatexchanger section 602 having first and second catalysts 72, 62 and ispreferably identical to the first heat exchanger section 502 of reactor500 except for the differences noted below. The reactor 600 alsoincludes a second heat exchanger section 604 which is preferablyidentical to section 504 of reactor 500 except where noted below.

In reactor 600 the outer shell section 512 is eliminated and at leastthe first heat exchanger section 502 is provided with a primary shell630 which is of enlarged diameter at least proximate to its primary end632. The primary shell 630 fits over a secondary inner shell 640 havinga first end 642 proximate the at least one opening 546 of the primaryshell 530 of the second heat exchanger section 604 and a second end 644which is rigidly secured to the flange 60 of tube sheet 58 of the firstheat exchanger section 602. The primary end 632 of the shell 630 isrigidly secured to the primary shell 530 of second section 604 below theopenings 546 so as to form a passageway 652 for flow of gas between thechambers 506 and 100 of the first and second heat exchanger sections 602and 604. It will be seen that an annular aperture 654 is formed betweenthe primary shell 630 and the second end 644 of the primary shell 530.Preferably, one or both of the openings 546 and 550 of heat exchanger600 are in the form of disconnected joints as described above withreference to FIG. 17. More preferably, at least opening 550 is in theform of a disconnected joint.

It will be appreciated by those skilled in the art of fuel reformersthat various modifications and changes can be made to the illustratedand described fuel reformer without departing from the spirit and scopeof this invention. Accordingly, all such modifications and changes asfall within the scope of the appended claims are intended to be includedwithin the scope of this invention.

1-70. (canceled)
 71. In a fuel conversion reactor, a shell-and-tube heatexchanger for heating a gaseous fluid prior to reaction with a fuel andfor cooling a gaseous mixture produced by the reaction, said heatexchanger comprising: (a) a first heat exchanger section comprising: (i)a first primary shell member having primary and secondary ends and asidewall extending between said ends and defining a first heatexchanging chamber located within the first shell member; (ii) a firsttube sheet fixedly mounted on said primary shell member in the vicinityof said primary end and sealingly closing said first heat exchangingchamber at one end of the first chamber; (iii) a second tube sheetdevice which is separate from said primary shell member and is locatedin the vicinity of said secondary end, said second tube sheet deviceforming another end of said first chamber that is opposite said one endof the first chamber; and (iv) a plurality of heat exchange tubesextending from said first tube sheet to said second tube sheet deviceand rigidly connected to both the first tube sheet and the second tubesheet device, said heat exchange tubes providing passageways for saidgaseous mixture to flow inside the tubes through said first heatexchanging chamber; and (v) one or more outlet apertures formed in theregion of said secondary end of said primary shell member in order toprovide at least one outlet for said gaseous fluid which flows throughsaid first heat exchanging chamber on a shell-side thereof duringoperation of said fuel conversion reactor; and (b) a second heatexchanger section comprising: (i) a second primary shell member havingprimary and secondary ends and a sidewall extending between said endsand defining a second heat exchanging chamber in communication with thefirst heat exchanging chamber, the second shell member being concentricwith the first shell member with the primary end of the first shellmember being located proximate the secondary end of the second shellmember; (ii) a plurality of heat exchanging tubes mounted in the secondshell member and communicating with the heat exchange tubes of the firstheat exchanger section; (iii) an inlet in the sidewall of the secondshell member for introducing the gaseous fluid into the second heatexchanging chamber; (iv) one or more outlet apertures formed in theregion of the secondary end of the second shell member to provide atleast one outlet for the gaseous fluid to flow from the second heatexchanging chamber to the first heat exchanging chamber.
 72. A fuelconversion reactor according to claim 71, wherein the first heatexchanger section further comprises one or more inlet apertures formedin the region of the primary end of the first shell member to provide atleast one inlet for the gaseous fluid to flow into the first heatexchanging chamber from the second heat exchanging chamber.
 73. A fuelconversion reactor according to claim 72, further comprising an outershell section having first and second ends surrounding the secondary endof the second shell member and the primary end of the first shell memberand forming a passageway for flow of the gaseous fluid from the secondheat exchanging chamber to the first heat exchanging chamber, the firstand second ends of the outer shell section being rigidly attached to therespective sidewalls of the first and second shell members, saidpassageway being formed between the outer shell section and the shellmembers.
 74. A fuel conversion reactor according to claim 73, whereinthe one or more outlet apertures formed in the region of the secondaryend of the second shell member are formed between the first and secondshell members.
 75. A fuel conversion reactor according to claim 74,wherein the one or more outlet apertures formed in the region of thesecondary end of the second shell member comprises a disconnected jointbetween the first and second shell members.
 76. A fuel conversionreactor according to claim 72, wherein the primary and of the firstshell member is of a greater diameter than the secondary end of thesecond shell member and wherein the secondary end of the second shellmember is received inside the primary end of the first shell member, andwherein the primary end of the first shell member is rigidly attached tothe sidewall of the second shell member such that a passageway for flowof the gaseous fluid from the second to the first heat exchangingchamber is formed between the first and second shell members.
 77. A fuelconversion reactor according to claim 76, wherein the one or more inletapertures comprise a continuous annular gap between the first and secondshell members.
 78. A fuel conversion reactor according to claim 76,wherein the one or more inlet apertures comprises a disconnected jointformed in the sidewall of the first shell member proximate its primaryend.